Isopropyl alcohol process



Oct. 27, 1953 A. P. GIRAlTls ET AL ISOPROPYL ALCOHOL PROCESS Filed Sept, 15, 1948 afm E zore oF lv mzmaodu Qmzdj mm Alm* Iv .du F

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@gfcf Sme-atm SSM C1 bb or' aeg Patented Oct. 27, 1953 2,657,243 IsoPRoPYL ALCOHOL PROCESS Albert P. Giraitis and Mack C. Fuqua, Baton Rouge, La., assignors to Standard Oil Development Company, a corporation of Delaware Application September l5, 1948, Serial N o. 49,450

Claims.

The quality of isopropyl alcohol is'improved economically by this invention through an industrially feasible method of purifying refinery propylene fractions.

The production of a high quality isopropyl alcohol product, from the standpoint of purity and odor, made by the hydration of propylene with sulfuric acid as catalyst, is achieved by removing C4 hydrocarbons from a propylene fraction prior to absorption in the acid; also, b-y removing simultaneously the highly unsaturated C3 hydrocarbons, methylacetylene and propadiene from the fraction.

'I'he production of a chemically pure isopropanol is desirable when the alcohol is to be used for preparing other chemicals, for use in cosmetics and toilet goods, for rubbing alcohol, or for use as a sterilizing agent.

The commercial propylene fraction is generally a cracked hydrocarbon product obtained by close fractionation which leaves the propylene contaminated by other C3 hydrocarbons and small amounts of C4 hydrocarbons.

The removal of the contaminants that cause degrading of the isopropyl alcohol product is eiiiciently accomplished by a method which will be further described in detail.

Earlier studies did not show any certain correlation between C4 components in the propylene feed stream to the acid absorber and the finished alcohol product. Now the failure to learn about this correlation can be ascribed to the rather long hold-up of impurities in the conventional alcohol plant operations.

Work has now been carried out to determine which, if any, of the C4 and C3 hydrocarbons, diicult to remove, produce the undesirable odor that often degraded the ispropyl alcohol product requiring an expensive washing and finishing treatment for removal.

In order to make the terms used understandable, a brief description of the process for isopropanol manufacture is given herewith. The propylene feed stock is fed at a suitable pressure to an absorber containing sulfuric acid of suitable strength and temperature and the sulfuric acid reacts with the propylene to form an isopropyl sulfate-sulfuric acid mixture also containing some free alcohol and isopropyl ether. This mixture is fed to a stripper where dilution Water is added and steam introduced to remove all alcohol and other volatile components from the diluted acid. After caustic scrubbing for removal of acidic components from the crude alcohol, the alcohol is sent to storage from which it is fed to the finishing section. The isopropanol finishing section consists of a column for removing low boiling impurities and some alcohol overhead and and alcohol-Water mixture with some impurities boiling higher than the alcohol as bottoms. The overhead stream is washed with water and the insoluble portion consisting primarily of isop-ropyl ether and high boiling impurities soluble in the ether is sent to storage. The water alcohol layer from this ether washer is returned to the above mentioned column for recovery of the alcohol. The bottoms from the above mentioned tower are fed to a second distillation tower for concentration and purification of the alcohol. Avportion of the lower boiling constituents from the column are recycled to the first column. This stream is referred to as recycle stock.

An isopropyl sulfate, sulfuric acid mixture of the usual strength made in the alcohol plants was prepared 'by adding sulfuric acid and Water to isopropyl alcohol of high grade with no odor. C4 hydrocarbons of different types were then absorbed in separate portions of the isopropyl sulfate-sulfuric acid mixtures to the extent of approximately l mole percent of propylene (or isopropyl alcohol) in the extract. The absorption was carried out by passing each of the gaseous C4 hydrocarbons through a separate sample of the extract at C. and atmospheric pressure until a predetermined amount was absorbed. One sample was allowed to absorb a large amount of one of the C4 hydrocarbons. Two control samples containing no C4 were prepared, one heated at 80 C. and the other at 100 C. for the same length of time and finished in the same Way as the other samples. 'I'he finished alcohol product was prepared from this steam distillate by distillation in the usual manner. The products of the samples were classied according to odor as follows:

Each of the samples, including even the control, produced a recycle stock that had odor, the recycle stock being the usual fractional condensate that is condensed from the overhead isopropyl alcohol vapors of the finishing still.

As shown by the foregoing experimentsp the absorption of the butylenes and of butadiene in the extract produced characteristic undesirable odor. The absorbed isobutane produced some odor. The strongest odors were approximately as strong as those obtained in plant production. It was notfound'howgto isolate the odoriferous compound or compounds. In studies made for the purpose of concentrating and possibly isolating the odoriferous products from the isopropyl alcohol product, isopropyl alcohol having odor Was carefully fractionated and separate small fractions were examined. It was foundlthat the odor components were both somewhat higher Vand Somewhat lower boiling than thefisopropylalcohol itself and could not be removed bygfractionation.

The adverse eifect of the C4 hydrocarbons'on odor is also usually accompanied by other undesired manifestations ysuch. as, acetone build up, increase of high boiling-compounds that accumulate inthe'fractionating tower plates above ,the feed Aplate in the valcohol .nishing istill, and lowered nishingrates.

AA plant scale vstudy ',Whichshovvs the necessity for making the ,propylene feed freeof C3 acetylenesrto produce ac high'vquality.isopropyl alcohol product isfurnished by thefollowing tabulated-dataof TableII:

The effects of.C4'hydrocarbons inthe propylene feed on lproduct quality and formation of undesired acetone .and vhigh boiling by-products Vis shown by data on typical plant runs presented in TableIII.

The data in Tables II and III indicate that the tolerable limit for both the C4 compounds and acetylenes in the C3 -feed is `not vmore than 0.10% and 0.05%, respectively, if Aa high quality alcohol is `to be obtained. They also show how the acetone and high `boiling ley-products increase as 5these impurities in the feed increase.

Thus it can be fully appreciated that van efcient method of reducing the Cs lacetylenecontent, preferably to less than 0.05%, -while reducing the C4 content ofthe C3 .propylene feed to less than 0.10% is a vvery important asset rfor producing high quality isopropyl alcohol economically.

`of the ffractional=distillation zone in T-I. #overhead vapor comprising the propylene and a 'smallproportion-of the C4 impurities that enter jT--lisWithdrawn by line 4. A bottoms product A satisfactory method for removing the harmful Ca and C4. hydrocarbon impurities of the propylene fraction will be described with reference to the accompanying iiow diagram.

In the drawing, the unit shown has two fractionating towers, low pressure tower ZT-l and high pressure tower T=2. The crude propylene fraction containing excessive amounts of the Aharmful Ca and C4 hydrocarbons, such as pres- -vent invia-.cracked hydrocarbon propane-propylene cut, is passed by line 3 into an intermediate part An comprising the C4 impurities is withdrawn from T--I-byrline 5.

The overhead vapor .from T-l is cooled and condensed-,by Vindirect :heat exchange 1 with @Water in condenser 15. A: .portion of the. overheadvapor condensate is returned .asxreflux by line .i .tozthe top of T-l and the remaining ,portionof condensateis passed byA-pumpCS-through line :9 into an intermediate part =of the .fractionating .zone of."I-2.

4In IL-2, the4temperaturealldpressure conditions are controlledto make .the liquidbottoms contain Ya substantial amount-.of Cmhydrocarbons with kthe yliquid C4 impurities, `so `that vapors that passgoverhead from .CF-2 throughline liraie essentially free of C3 acetylene and .C4 ,hydrocarbons. The voverhead vaporszfrom -I-.2 .-arepartially Acondensed in water cooled condenser vH. The condensatacollectsin receiver l2 and isreturned by pump I3 and Aline y,Ill asrefluxtmthe top of T-Z. Puried Dropylenelproductisrvvithdrawn from Yreceiver i2 by line-[5to be passed to an alcohol Aproducing -unit, e. .g., into a sulfuric acid absorption tower. .The bottoms withdrawn Vfrom TIL-f2 `.are recycled .by lpump -lB through line Il tothelow .pressure tower fI-i.

The Vtowers .T-i and T--2 areequippedrwith vapor-liduid contacting means, ve. g., `plates .I8 and 1S, reboiling heat exchangers .20 and 2l ,and other usual fractionating towerequiprnent.

For the Atypeof .operation described, suitable conditionsin the fractionating zones-are:

The temperatures.v and pressuresgivemare close approximations .but may vary vslightly iwith the feed composition. In general, fthe 'top temperature .of :both 'towers .is held preferably zat Aabout .130 the ypressure for '.T-i is in the irange of 3.00 to '330"p.1s.;i. g. with a Ill-.i :bottomitemp erature in .thezrange of 240 `,to .25.5 ,.F.; andthe pressure for T11-f2 is in .therange `of :.330 :to .350 p. is. i. g. :with :a Y'1L-2 bottom .temperature kin :the rangeof 180to220 F.

In operating -thetowers at `the higher .part .of their Ipressure, ranges, .the bottoms liquid-recycled from thegpressuretower 'IL-.2 to .Tf-E will contain 3D .to 80% .by weight `of `liquid C3 :hydrocarbons (propylene -and propane). In operating ,the towers in .the lower part of ltheirpressure-ranges the bottoms liquid recycled. from T-2 .to T-I -Will contain i0 -to 30% by weight of these .liquid C3 hydrocarbons.

The yQperation :in the Alower `part of .the presin which a sure ranges is permitted when the initial feed has a low content of the Cs acetylenes and C4 hydrocarbons, e. g., 0.1 to 0.2 Weight per cent, and such a feed may be supplied to the unit through line 22 so as to enter the high pressure tower T-Z first.

In the operations described the C3 acetylenes are present in the C4 bottoms withdrawn from the low pressure tower T-I, but if desired a portion of the bottoms liquid passed from T-Z to T-I may -be purged or treated to obtain a selective removal of acetylenes.

The invention claimed is:

1. The process of separating C4 hydrocarbons and Cs acetylene contaminants from a C3 hydrocarbon propylene fraction to obtain purified propylene suitable for producing high quality isopropyl alcohol, which comprises distilling substantially all propylene and propane from said fraction together with a minor portion of the C4 hydrocarbons in a fractional distillation zone, passing thus distilled hydrocarbons into a higher pressure fractional distillation zone, condensing substantially all C4 hydrocarbons and acetylenes with a substantial portion of Cs hydrocarbons in said higher pressure fractional distillation zone, withdrawing overhead from said higher pressure fractional distillation zone propylene vapors substantially free of acetylenes and C4 hydrocarbon impurities, returning to the iirst mentioned fractional distillation zone lifuid bottoms from the higher pressure fractional distillation zone, and removing separated C4 hydrocarbons and C3 acetylenes in liquid bottoms withdrawn from the first mentioned fractional distillation zone.

2. In the preparation of a propylene feed suitable for hydration to odorless isopropyl alcohol, the steps of separating C4 hydrocarbon impurities from a C3 hydrocarbon fraction of propylene and propane, which comprises distilling from said C3 hydrocarbon fraction substantially all its propylene and propane components with a minor amount of the C4 hydrocarbons under a pressure in the range of 300 to 330 pounds per square inch gauge, passing resulting distillate from said fractional to a higher pressure fractional distillation zone, distilling propylene and propane substantially free of C4 hydrocarbons from the distillate in said higher pressure fractional distillation zone at a pressure in the range of 330 to 350 pounds per square inch gauge, passing bottoms liquid containing a substantial amount of Ca hydrocarbons from said higher pressure fractional distillation zone to the rst mentioned fractional distillation zone, and withdrawing bottoms liquid containing separated C4 hydrocarbons from said rst mentioned fractional distillation zone.

3. The process of separating Cs acetylenes and C4 hydrocarbon impurities from a C3 hydrocarbon fraction of propylene and propane, which comprises fractionally distilling propylene and propane with a minor portion of said impurities under a pressure in the range of about 300 to 330 pounds per square inch gauge in a fractional dis- F., refluxing a portion of the resulting d1stillate in the upper part of said fractional intermediate part pressure fractional distillation zone pressure of 330 to 350 pounds per square inch gauge is maintained with top temperature of 130 F. and a bottom temperature in the range of 180 to 220 F., removing propylene to an upper and propane vapors from said higher pressure fractional distillation zone, partially condensing overhead vapors from said higher pressure fractional distillation zone into condensate, separating uncondensed propylene and propane vapors from said condensate, refluxing said condensate part of said higher pressure fractional distillation zone, passing bottoms liquid from the higher pressure fractional distillation zone into said rst mentioned fractional distillation zone and withdrawing liquid bottoms containing separated Ci hydrocarbons and Ca acetylenes therefrom.

4. In a production of high quality isopropyl alcohol from propylene in the presence of sulfuric acid, the steps of pretreating a propylene fraction that contains small amounts of `C4 hydrocarbons and `Ca acetylenes as impurities which comprises distilling the propylene from said fraction with a minor portion of said impurities in a zone under a pressure which maintains the major portion of the `C4 hydrocarbons and the Cla acetylenes in liquid phase, passing the distilled propylene with said distilled impurities into a higher pressure fractional distillation zone, maintaining a substantial portion of the propylene in liquid phase with said impurities in said higher pressure fractional distillation zone, withdrawing overhead from said higher pressure fractional distillation zone a propylene-rich fraction substantially free of said impurities for hydration to the alcohol, withdrawing from said higher pressure fractional distillation zone a liquid residue containing liquid propylene with said impurities, passing said liquid residue from said higher pres- Sure to Said relatively lower pressure fractional distillation zone, and withdrawing said impurities in liquid phase from saidrelatively lower pressure fractional distillation zone.

5. In the production of high quality isopropyl alcohol by hydration of propylene in the presence of sulfuric acid, the steps of separating by distillation a propylene-rich fraction containing between 0.1 and 1% by weight of C4 hydrocarbons and from 0.05 to 0.15% Ca acetylenes from a commercial propylene fraction, partially condensing under increased pressure from said propylene-rich fraction a condensate containing 10 to 60 weight per cent of lC3 hydrocarbons with a portion of the C4 hydrocarbons and Ca acetylenes so as to leave the remaining propylene-rich vapor fraction with a C4 hydrocarbon content of less than 0.1 weight per cent and a C3 acetylene content of less than 0.05 weight per cent.

ALBERT P. GIRAITIS. MACK C. FUQUA. References Cited in the lle of this patent UNITED STATES PATENTS Number Name Date 1,465,600 Eldred Aug. 21, 1923 1,957,818 Carney May 8, 1934 2,055,720 Francis Jan. 9, 1940 2,222,276 Babcock Nov. 19, 1940 2,370,948 Gad-wa Mar. 6, 1945 2,409,773 Luten Oct. 22, 1946 2,431,685 Cade Dec. 2, 1947 2,514,294 Rupp July 4, 1950 FOREIGN PATENTS Number Country Date 297,842 Great Britain Aug. 1, 1929 586,831 Great Britain Apr. 2, 1947 

5. IN THE PRODUCTION OF HIGH QUALITY ISOPROPYL ALCOHOL BY HYDRATION OF PROPYLENE IN THE PRESENCE OF SULFURIC ACID, THE STEPS OF SEPARATING BY DISTILLATION A PROPYLENE-RICH FRACTION CONTAINING BETWEEN 0.1 AND 1% BY WEIGHT OF C4 HYDROCARBONS AND FROM 0.05 TO 0.15% C3 ACETYLENES FROM A COMMERCIAL PROPYLENE FRACTION, PARTIALLY CONDENSING UNDER INCREASED PRESSURE FROM SAID PROPYLENE-RICH FRACTION A CONDENSATE CONTAINING 10 TO 60 WEIGHT PER CENT OF C3 HYDROCARBONS WITH A PORTION OF THE C4 HYDROCARBONS AND C3 ACETYLENES SO AS TO LEAVE THE REMAINING PROPYLENE-RICH VAPOR FRACTION WITH A C4 HYDROCARBON CONTENT OF LESS THAN 0.1 WEIGHT PER CENT AND A C3 ACETYLENE CONTENT OF LESS THAN 0.05 WEIGHT PER CENT. 